Process for the preparation of alkylglycoside esters

ABSTRACT

In a process for the manufacture of C 1  -C 18  alkylglycoside ester of C 4  -C 24  fatty acids, the reactants are first formed into a stable micro-emulsion before they are contacted with an enzyme catalyst. The stable micro-emulsion is prepared, using a surface-active material, which is preferably the alkylglycoside ester formed.

The present invention relates to a process for the manufacture ofalkylglycoside esters, in which an alkylglycoside and an acyl groupdonor are contacted with an enzyme catalyst.

Such a process is known from e.g. PCT patent applications WO-B-8901480and WO-B-9009451, as well as from Synthesis, February 1990, pp. 112-115and J. Chem. Soc., Chem. Commum., 1989, pp. 934-935.

In these publications, processes are described for the enzyme catalysedpreparation of 6-0-acylglucopyranosides by simply mixing the startingalkylglycoside with a fatty acid at 70° C. in the presence of animmobilized lipase. The water generated in the reaction is removed invacuo. In this way, using a species of Candida antarctica, yields of85-95% of the 6-0-monoesters were obtained. Although a suitable solvent,such as hexane or acetonitrile may be used, such solvent will generallyinactivate the enzyme, and they are toxic, which is detrimental to theenvironment and requires a thorough purification of the end product, ifthis has to be used in food or cosmetic applications.

A problem in the processes thus described is the high viscosity of thealkylglycoside, which needs to be mixed with the molten fatty acid,which is very difficult and increases the total reaction timeconsiderably. Also if the amount of acyl donor is increased relative tothe alkylglycoside to increase the reaction efficiency, by-products,such as diesters tend to be formed in appreciable amounts.

There is therefore still a need for a process for the manufacture ofalkylglycoside esters having a high monoester content at a high reactionrate, without the problems as outlined above.

It is an object of the present invention to provide a process for themanufacture of alkylglycoside esters, in which an alkylglycoside and anacyl group donor are contacted with an enzyme catalyst, in which in arelatively short time alkylglycoside monoesters of high purity areformed.

During extensive investigations it has been found that if thealkylglycoside and the acyl donor are mixed with a surface activematerial, preferably with an effective amount of the alkylglycosideester formed, a stable micro-emulsion is formed, which is very easy tohandle throughout the whole manufacturing process. By "a micro-emulsion"is understood throughout this specification and the attached claims adispersed system stabilized by surfactants which could be micellarsystems or true micro-emulsions. By changing the ratio of acyl donor toalkylglycoside it appeared to be possible to control the viscosity ofthe micro-emulsion, whereas the stability of the micro-emulsion could becontrolled by the amount and (to a lesser extent) the type ofsurface-active material used. A molar ratio of acyl donor toalkylglycoside of 1.0-2.0 moles of acyl donor per mole of alkylglycosideis preferred.

It has been stated in U.S. Pat. No. 4,614,718 (Seino et al.) that sugaror sugar-alcohol fatty acid esters have been prepared by dispersing alower alkyl ester of a fatty acid in a solution of sugar in a solvent,such as propylene glycol or water, with the aid of an emulsifier, suchas soap, after which the solvent is removed before thetransesterification reaction is started. This process is said to beknown as the "microemulsion process" (see U.S. Pat. No. 4,614,718,Column 1, lines 17-22). This is a non-enzymatic process, however, andSeino et al. clearly state that this method exhibits seriousdisadvantages, such as the high reaction temperature, leading todiscoloration and the use of solvents. The "micro-emulsion process" hasbeen described in detail in Journal of the American Oil Chemists'Society, Volume 44, No. 5 (May 1967), 307-309. In this publication ithas been described how sucrose dissolved in propylene glycol, methylstearate, sodium stearate and potassium carbonate catalyst are combinedto form a transparent micro-emulsion. On page 309 it has been statedthat this micro-emulsion is formed at 130°-135° C., and that themicro-emulsion is not stable at room temperature.

In the process according to the present invention the micro-emulsionscan be formed at room temperature and they are indefinitely stable. Thisstability is an advantage because it is possible to preform themicro-emulsion and then store it, without any danger that it will changein character or composition through precipitation or phase separation.Also no heating treatment is required which may impair the colour of theproduct.

Also in the Osipow et al. process the solvent is left in the systemuntil it is distilled out during the course of the reaction, andmoreover potassium carbonate is used, which helps to form the anionicsurfactant needed to stabilise the micro-emulsion and which is essentialas a catalyst. In the process of the present invention the catalyst hasno role whatsoever in the micro-emulsion process and the solvent isremoved, to leave a very stable micro-emulsion.

Therefore the present invention relates to a process for the manufactureof alkylglycoside esters, in which an alkylglycoside and an acyl groupdonor are contacted with an enzyme catalyst, which is characterized inthat a stable micro-emulsion is formed from the reactants, before thereactants are contacted with the enzyme catalyst using a surface-activematerial.

The stable micro-emulsion of the reactants can be prepared in a numberof ways, which are to a certain extent dictated by the type and relativeamounts of the reactants. It is possible to take the acyl donor and thealkylglycoside, add the surface-active material and to stir the mixtureobtained vigorously. Dependent on the type of alkylglycoside and theacyl donor and their relative amounts, this will still take some timedue to the viscous nature of the alkylglycoside, but already animprovement in the process is obtained in this way, because of the highcontact surface offered by the micro-emulsion to the enzyme catalyst inthe next step of the process.

It has been found advantageous, however, to dissolve the alkylglycoside,the acyl donor and the surface-active material in a common solvent,which is preferably innocuous, such as ethanol, whilst stirring. Whenthe solvent is evaporated from the homogeneous solution, themicro-emulsion forms spontaneously. The evaporated solvent can becondensed and recycled into the process. Suitable solvents are the loweralkanols having up to four carbon atoms and polyhydric alcohols, such asglycols, or glycerol, but preferably a solvent is used having a boilingpoint below about 100° C., which is innocuous. The micro-emulsion ispreferably formed between room temperature (15° C.) and 80° C.

In a particularly preferred embodiment of the present invention, anexcess of alcohol is used in the previous production of thealkylglycoside, so that a mixture of alkylglycoside and alcohol isobtained. This mixture is then mixed with the acyl donor and thesurface-active material (preferably the alkylglycoside ester formed) andwhilst stirring, the excess alcohol is then removed by distillation orevaporation, after which a stable micro-emulsion is obtained. Thus, forexample, with 5% by weight of ethylglucoside dodecanoic acid ester,dodecanoic acid and ethylglucoside, finally an emulsion was obtainedhaving a viscosity of 300-400 cP at 60-80° C.

Preferably the surface-active material is the alkylglycoside ester whichis formed in the process and an effective amount of the ester formed iscontinuously recycled into the process for the formation of the stablemicro-emulsion.

It is also possible to form the stable micro-emulsion, using other,preferably nonionic and/or anionic surface-active agents, such as fattyacid monoglycerides, polyglycerol fatty acid esters, fatty acid sodiumor potassium soaps, sugar esters, sugar alcohol esters; sodiumbis(2-ethylhexyl) sulfosuccinate; other alkylglycoside esters than thoseformed in the reaction; alkylpolyglycosides and mixtures thereof.

Preferably the surface-active agent or mixture thereof is innocuous orfood grade. In general no surface-active agents are used which under theconditions of the reaction will participate in the reaction.

After the micro-emulsion has been formed, the enzyme catalyst can beadded to it whilst stirring and keeping the mixture at about 30° C. to80° C., whilst also applying a vacuum to remove the water produced inthe esterification reaction. The reaction mixture can, for example, becirculated through an external evaporator (falling or wiped filmreactor) to facilitate the removal of the water of esterification, butalso to remove the alcohol used in the formation of the micro-emulsion.

It is known to immobilize enzyme catalysts, which usually includescross-linking of cell homogenates, coating on a solid particulatesupport, such as plastics, polysaccharides, ion exchange resins,silicates (glass), entrapment in gels and the like. Such immobilizedenzyme catalysts have the advantage of being easily to separate.Surprisingly, the present invention enables the use of the enzymecatalyst in the form of a solution or dispersion. The use of themicro-emulsion will allow easy and highly effective dispersion of theenzyme catalyst in the reaction mixture, with almost each enzymemolecule in a different micro-emulsion droplet. This leads to fastreaction rates with a high degree of conversion.

It has been disclosed in European Patent Application EP-A-0,334,498(Cerestar Holding BV) to prepare esters of alkylglucosides by using anon-immobilised enzyme catalyst, but first of all, the reaction timesvary from 24 to 120 hours and more important the yields are not higherthan 50%.

The reaction technique as embodied by the present invention does lead toshort reaction times and very high yields of almost pure product.

The enzyme catalyst is a catalyst which is active in the hydrolysis ofester bonds and therefore is a hydrolase. The enzyme catalyst preferablyis selected from the group consisting of lipases (e.g. porcine pancreaslipase or microbial lipases), esterases or proteases. The use ofthermostable lipases, such as derived form Candida antarctica asdescribed in PCT application WO-B-8802775 (Novo Industri) or derivedfrom Mucor miehei is preferred.

If the enzyme catalyst is used in immobilized form, a preferredembodiment of the process according to the present invention is to formthe micro-emulsion of the reactants with the surface-active material,preferably from a starting solution in a common solvent as referred toearlier, after which the micro-emulsion is pumped through one or morebeds packed with the enzyme catalyst immobilised on a suitable supportmaterial. Between the reactors, the water produced in the reaction isremoved, suitably by passing the reaction mixture through a falling orwiped film evaporator, to ensure that the esterification reductionreaches the required, high degree of conversion. This embodiment, usinga packed bed reactor would, without the use of the micro-emulsiontechnique according to the present invention technically not have beenfeasible.

The alkyl group of the alkylglycoside may be a saturated or unsaturated,straight or branched chain alkyl group, having from 1 to 18 carbonatoms. The alkyl group may be substituted with functional groups, suchas hydroxyl groups. The use of a saturated, straight chain alkyl group,having from 1 to 8 carbon atoms is preferred.

The glycoside part of the alkylglycoside comprises from 1 to 3monosaccharide units. These monosaccharide units preferably are in thepentose or hexose from (particularly the furanose or pyranose form).Suitable monosaccharides are arabinose, ribose, xylose, xylulose,lyxose, rubulose and 2-deoxyribose, glucose, fructose, galactose,mannose, sorbose, talose and deoxy sugars, such as 2-deoxyglucose,6-deoxygalactose, 6-deoxymannose and 2-deoxygalactose. Preferreddisaccharides are maltose, isomaltose, sucrose, cellobiose, lactose andsophorose. Also various hepturoses, such as glucohepturose,arohepturose, sidohepturose and mannohepturose may be used. Mixtures ofalkylglycosides may also be used.

The acyl group donor is selected from the group consisting of saturatedor unsaturated, straight or branched chain fatty acids having from 4 to24 carbon atoms. The fatty acids may also comprise functional groups,such as hydroxyl groups, halogen atoms and like other groups.

Another group of acyl donors are the esters of the said of fatty acidswith alkanols having from 1 to 8 carbon atoms. Finally the acyl groupdonor may be a monoglyceride, diglyceride and/or triglyceride of thesaid fatty acids. Mixtures of acyl group donors may also be used. Theuse of free fatty acids and C₁ -C₃ alkyl esters of said fatty acids ispreferred.

Also fatty acid oxime esters can be used as the acyl donors.

The reaction temperature at which the reactants micro-emulsion iscontacted with the enzyme catalyst ranges from 20° C. to 110° C.,preferably from about 30° C. to 80° C.

In order to remove any solvent or the water of esterification formed inthe reaction, the process according to the present invention ispreferably carried out at sub-atmospheric pressure (vacuum).

The alkylglycoside esters prepared by means of the process according tothe present invention may advantageously be use in detergentcompositions, in cosmetic products and compositions and in foodstuffs orfood additive compositions.

The invention is now further illustrated by the following examples.

EXAMPLE I

In this example the generation of stable micro-emulsions fromethylglucoside, fatty acid and surfactant has been described.

A mixture of 60 g lauric acid, 52 g of ethylglucoside and 5.6 g of asurfactant were dissolved in 100 ml of ethanol. The solvent was thenevaporated from the mixture using a rotary evaporator and the stabilityof the mixture left, when all the solvent had been removed, wasassessed. When a stable micro-emulsion system is formed, the systemremains homogeneous, whereas in cases where no micro-emulsion is formed,it can be clearly seen that the system separates into two distinctphases.

The following surfactants were found to give stable micro-emulsions:

alkylpolyglucosides, made from decanol and dodecanol with an averagedegree of polymerization of the polyglucoside of 1.4; 20 grams of a 28wt % solution of sodium lauryl ethersulphate in water; sodium laurylsulphate; sodium dihexylsulphosuccinate.

EXAMPLE II

A solution of an alkylpolyglucoside (33 g, derived from directly fromdecanol and glucose by a standard procedure as described in U.S. Pat.No. 3,839,318) in ethanol (50 ml) was added to a mixture ofethylglucoside (312 g) and lauric acid (360 g) contained in a roundbottomed flask fitted with a stirrer and a condenser.

A further portion of ethanol (100 ml) was added and the mixture waswarmed to 70° C. and maintained at this temperature until all thematerials had dissolved. Once the solution was homogeneous the ethanolwas removed, by distillation, and supported lipase enzyme (SP 435, exNovo Nordisk A/S, 33 g slurried with 33 mls water) was added to theresulting homogeneous mixture.

After the enzyme had been added, the reaction mixture was heated to 75°C. and stirred under vacuum to remove the water formed in theesterification reaction. The reaction was followed by HPLC and after 23hours reaction time 80% conversion of the ethylglycoside to the esterwas seen.

EXAMPLE III

A solution of ethylglucoside (30%) in ethanol (500 kg ethylglycoside)was pumped into an autoclave fitted with a condenser, vacuum system andstirrer and the ethanol was removed by distillation to leave a viscoussyrup. Molten lauric acid (540 kg, Unichema Prifac 2922; ™) was addedand the mixture was maintained at 70° C. and stirred for 4 hr afterwhich the reagents were still not fully mixed. A thick layer ofethylglucoside remained in the bottom of the autoclave. Enzyme (Novo SP435, 50 kg) was added and the system was maintained at 75° C. undervacuum (10 mbar) for 24 hours. After 6 h the reaction mixture washomogeneous and analysis by HPLC showed that the ethylglucoside wasconverted to the lauric acid ester (85% conversion after 15 h). Thisexample clearly shows the advantage of generating the homogeneousmicro-emulsion in solution.

EXAMPLE IV

The procedure of Example III was repeated with the following changes:before the alcohol was distilled from the ethylglucoside, 50 kg of theester, prepared in the previous reaction was added. The fatty acid wasadded as the alcohol was distilled from the reactor and at the end ofthe distillation the reaction mixture was a mobile syrup that could bestirred without difficulty.

EXAMPLE V

C₁₂ fatty acid ethylglucoside ester (13.0 g) and ethylglucoside (112.0g) were weighed into a 500 ml round-bottom vessel and mixed at 80° C. bystirring with an impeller. Lauric acid (130.4 g) (Prifrac 2920, exUnichema International Trade Mark) was added to the vessel and furtherstirring for 2 hours at 80° C. and a pressure of 20 mbar produced amicro-emulsion and, in addition, removed residual ethanol from thereaction mixture. At this point samples were removed from the vessel foranalysis by HPLC and for acid value determination.

The temperature of the reaction mixture was reduced to 60° C. and thepressure to 10 mbar. A solution of Candida antarctica lipase B (800 mg)(SP 434, ex. Novo Nordisk, activity=200 KLU/g) in distilled water (6 ml)was added to the contents of the vessel. Stirring (at 250 rpm) wascontinued and further samples were removed for HPLC analysis and foracid value determination if required. The reaction was terminated after23 hours. The compositions of the reaction mixture in wt % at variousreaction times are given in Table 1. After 23 hours the yield ofethylglucoside ester was 90% based on ethylglucoside.

Samples taken for analysis by HPLC were weighed into vials. After a caphad been fitted, each vial was immersed in boiling water for at least 30minutes to deactivate the enzyme in the sample. The deactivated sampleswere dissolved in known amounts of 96% aqueous ethanol and analysed byHPLC to determine the concentration of ethylglucoside ester andethylglucoside in each sample.

                  TABLE 1                                                         ______________________________________                                        Reaction Time                                                                             EGE         EG      LA                                            (hours)     (wt %)      (wt %)  (wt %)                                        ______________________________________                                        0            4.2        37.8    51.1                                          1.0         13.0        30.6    --                                            2.0         --          --      --                                            2.5         28.2        26.4    --                                            3.0         --          --      --                                            3.5         34.0        23.8    --                                            4.0         --          --                                                    4.5         40.5        18.2    --                                            5.0         --          --      --                                            5.5         43.9        17.0    --                                            6.0         --          --      --                                            23.0        67.3         4.5    26.1                                          ______________________________________                                         NB EGE = C.sub.12  ethylglucoside ester                                       EG = ethylglucoside                                                           LA = lauric acid                                                         

The rate of synthesis of ester over the first five hours isapproximately linear with respect to time and was over this time period67 mmol ester/hour/g of enzyme.

EXAMPLE VI

Example V was repeated, but in this experiment, an amount of the esterproduct was not added to the vessel prior to the addition of the enzyme.Therefore, a micro-emulsion did not form in the reaction mixture until arequisite amount of ester had been synthesised in the vessel. As withthe first experiment, a lauric acid: ethylglucoside molar ratio of 1.2:1was employed.

Ethylglucoside (112.5 g) and lauric acid (131 g) were weighed into around-bottom vessel. Residual ethanol was removed as before by stirringfor 2 hours at 80° C. and 20 mbar. Candida antarctica lipase B (800 mg)in distilled water (6 ml) was added and contents of the vessel werestirred at 60° C. and about 15 mbar. Initially, the viscosity of thereaction mixture was too high for samples to be removed by pipette foranalysis. However, from two hours onwards samples were taken following areduction in viscosity. The compositions of the reaction mixture atvarious reaction times are given in Table 2.

After 23 hours the yield of ethylglucoside ester was about 90% based onethylglucoside. Then also the rate of synthesis of ester over the firstfive hours is approximately linear with respect to time, but the rateover this period was 50 mmol ester/hour/g of enzyme, suggesting a fasterreaction rate by the formation of a micro-emulsion prior to the additionof enzyme.

                  TABLE 2                                                         ______________________________________                                        Reaction Time                                                                 (hours)     EGE          EG     LA                                            ______________________________________                                        0           0            39.3   53.8                                          1.0         --           --     --                                            2.0         13.2         31.4   --                                            2.5         --           --     --                                            3.0         19.6         28.0   --                                            3.5         --           --     --                                            4.0         25.5         24.9   --                                            4.5         --           --     --                                            5.0         31.2         23.0   --                                            5.5         --           --     --                                            6.0         35.9         20.9   --                                            23.0        67.9          5.6   26.4                                          ______________________________________                                         NB EGE = C.sub.12  ethylglucoside ester                                       EG = ethylglucoside                                                           LA = lauric acid                                                         

We claim:
 1. In a process for the manufacture of alkylglycoside esters,in which an alkylglycoside and an acyl group donor are contacted with anenzyme catalyst, the improvement wherein a stable micro-emulsion isformed by mixing the reactants and surface-active material before thereactants are contacted with the enzyme catalyst and only thereaftercontacting the enzyme with said micro-emulsion.
 2. A process accordingto claim 1 wherein the stable micro-emulsion of the reactants is formedby using an amount effective to form said micro-emulsion of the producedalkylglycoside ester as the surface-active material.
 3. A processaccording to claim 1, wherein the surface-active material is selectedfrom the group consisting of fatty acid monoglycerides, polyglycerolfatty acid esters, sugar alcohol esters, alkylglycoside esters,alkylpolyglycosides, and mixtures thereof.
 4. A process according toclaim 1, wherein the stable micro-emulsion of the reactants is formed bydissolving the acyl group donor, the alkylglycoside and thesurface-active material in the same solvent, after which the solvent isremoved from the homogeneous solution.
 5. A process according to claim4, wherein the solvent is selected form the group consisting of C₁ -C₄alkanols, polyhydric alcohols, and mixtures thereof.
 6. A processaccording to claim 1, in which the micro-emulsion is formed between roomtemperature and 80° C.
 7. A process according to claim 1, wherein thestable micro-emulsion is contacted with an immobilized enzyme.
 8. Aprocess according the claim 1, wherein the stable micro-emulsion iscontacted with an enzyme immobilized in the form of a packed bed.
 9. Aprocess according to claim 1, wherein the enzyme catalyst is dispersedin the form of a solution or dispersion into the stable micro-emulsion.10. A process according to claim 1, wherein the enzyme catalyst is ahydrolase.
 11. A process according to claim 1, wherein the enzymecatalyst is selected form the group consisting of lipases, esterases,proteases and mixtures thereof.
 12. A process according to claim 1,wherein the alkyl group of the alkylglycoside is a saturated orunsaturated, straight or branched chain alkyl group having 1-18 carbonatoms.
 13. A process according to claim 1, wherein the alkyl group ofthe alkylglycoside is a saturated, straight chain alkyl group having 1-8carbon atoms.
 14. A process according to claim 1, wherein the glycosidepart of the alkylglycoside comprises 1-3 monosaccharide units.
 15. Aprocess according to claim 1, wherein the glycoside part of thealkylglycoside is selected form the group consisting of glucose,fructose, galactose, xylose, ribose, mannose, arabinose, lactose,maltose, isomaltose, sucrose, cellobiose, arabinose, xylulose, rubulose,2-deoxyribose, sorbose, talose, 2-deoxyglucose, 6-deoxygalactose,6-deoxymannose, 2-deoxygalactose, sophorose, arohepturose,sedohepturose, mannohepturose, glucohepturose and mixtures thereof. 16.A process according to claim 1, wherein the acyl group donor is selectedfrom the group consisting of saturated or unsaturated, straight orbranched chain C₄ -C₂₄ fatty acids, C₁ -C₈ alkyl esters of said fattyacids, glycerol esters of said fatty acids, and mixtures thereof.
 17. Aprocess according to claim 1, wherein the reactants are contacted withthe enzyme catalyst at a temperature of from 20° C. to 110° C.
 18. Aprocess according to claim 1, wherein the reactants are contacted withthe enzyme catalyst at sub-atmospheric pressure.
 19. A process accordingto claim 17 wherein the temperature of contact is from 30° C. to 80° C.20. A process according to claim 1 wherein the micro-emulsion consistsof the alkylglycoside, acyl group donor and surface-active material.